Susan Lin, Pam Beddor and Andries Coetzee published “Gestural reduction, lexical frequency, and sound change: a study of post-vocalic /l/” in Laboratory Phonology's special issue on "The relationship between the origin and spread of sound change."
Citation: Susan Lin, Pam Beddor and Andries Coetzee (2014) “Gestural reduction, lexical frequency, and sound change: a study of post-vocalic /l/.” Laboratory Phonology 5:1, 9-36.
Abstract: The magnitude of anterior and dorsal constrictions for laterals in /(C)(C)VlC/ words produced by eight American English speakers was measured using ultrasound imaging. The results replicate previous findings that laterals have weaker anterior constrictions when followed by labial or velar consonants than when followed by alveolar consonants. The main novel finding is that, in words with /VlClabial/ or /VlCvelar/ sequences, this anterior constriction was weaker in high-frequency words (help, milk) than in low-frequency words (whelp, ilk). Although high-frequency words also showed slight reduction of the dorsal constriction, dorsal reduction was stable, small in magnitude, and not correlated with anterior reduction, consistent with alveolar reduction not being simply a consequence of overall weaker lingual constrictions in more frequent words. Acoustic measures for laterals showed that the degree of anterior constriction correlated with the frequency separation between F1 and F2: more reduced alveolar constrictions – especially likely in high-frequency words – were linked with greater formant proximity. These articulatory and acoustic patterns are interpreted as potentially contributing to the initiation and lexical diffusion of historical /l/ lenition. It is proposed that gestural reduction in high-frequency words in which the anterior gesture for laterals must be coordinated with another supralaryngeal constriction serves as a precipitating factor in /l/ vocalization and possibly (although to a lesser extent) /l/ loss.